日本結晶学会誌
Online ISSN : 1884-5576
Print ISSN : 0369-4585
ISSN-L : 0369-4585
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中性子結晶構造解析で明らかになったビリン還元酵素PcyA基質複合体の2つの水素化状態と構造的特徴
海野 昌喜杉島 正一和田 啓萩原 義徳日下 勝弘玉田 太郎福山 恵一
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2015 年 57 巻 5 号 p. 297-303

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Bilin compounds are fundamentally important for oxygenic photosynthetic organisms, because they are utilized as pigments for photosynthesis (phycobilins) and photoreceptors (phytochromobilin). Phycocyanobilin (PCB), a phycobilin, comprises the chromophore of algal phytochromes and the core phycobiliprotein antennae of cyanobacteria and red algae. PCB is biosynthesized by a member of the ferredoxin-dependent bilin reductase family, phycocyanobilin:ferredoxin oxidoreductase (PcyA). In the present study, we determined the neutron crystal structure of PcyA in complex with its substrate biliverdin (BV). This neutron structure revealed the protonation state of BV and the surrounding residues. We found that two forms of BV, neutral BV and protonated BVH+, were coupled with the two conformation/protonation states of the essential residue Asp105. Further, His88 and His74 near BV were singly protonated and were connected with an intervening hydronium ion. Neutron analysis also revealed how X-ray irradiation of the PcyA-BV crystal altered the structure of the PcyA-BV complex.

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